This invention relates in general to the field of munitions, and more specifically to the safing and arming of explosive shells or projectiles fired at high velocities from an internally-rifled gun.
Systems comprising an explosive shell typically consist of a fuze assembly, including an antenna, radar system, battery, and safing and arming device, as well as a detonator, detonator booster and high explosives. The safing and arming device within the fuze is designed to provide a safe separation distance from the gun launch site to the site of actual arming of the explosive shell. Generally, at least two independent means within the safing and arming device are employed to ensure safe operation.
One type of safing and arming device is termed "in-line", referring to a linear configuration of a detonator, barrier, and detonator booster and high explosive. The barrier, which is a component of the safing and arming device, is locked in an obstructing position between the detonator and the detonator booster and high explosive, providing a safe configuration when the shell is fired. The barrier is subsequently removed at a predetermined time by the action of the safing and arming device, thereby allowing the detonator to trigger the detonator booster and high explosive at a predetermined time.
Many traditional electro-mechanical safing and arming devices rely on a source of electrical power, such as a battery, to perform arming using a piston actuator and an electrical detonator. Disadvantages of such safing and arming devices, particularly in small, e.g. 35-millimeter caliber weapons, can be undependability and high cost. Batteries occupy a significant amount of space and require recharging or replacement after time. Even in systems where a battery is required to power other fuze components (and thus cannot be omitted from the fuze assembly), the battery can be reduced in size and weight by the use of a non-electrical safing and arming device. Furthermore, electrical connections in electrical safing and arming devices are subject to high stress during acceleration and spin and represent an additional possible mode of failure for the safing and arming device.
Typical mechanical safing and arming devices, especially if complex, can also be undependable and intolerant of rough handling. This is true particularly where the devices employ delicate mechanisms such as escapements. Some mechanical safing and arming devices also use mechanisms that cannot be tested and reused. Testing and reuse is important in producing safing and arming devices with well-known characteristics.
Finally, neither electrical nor mechanical safing and arming devices generally provide protection with respect to the omission during manufacture of the safing and arming device barrier from the fuze assembly. An unsafe condition results from such an omission because the obstruction between the detonator and high explosive is a principal safety means of the device. Without the barrier "fail safe" provision, a single contingency, such as the accidental firing of the detonator, could explode the shell.
An additional constraint on safing and arming devices is that the current United States military standard relating to the safety of weapon fuze designs (MILL-STD-1316D) requires that no stored energy be used in the arming process. Thus, no spring-actuated mechanisms or stored potential-energy driven systems are permissible in current U.S. safing and arming devices.